Although useful advances are being made in energy saving devices such as organic-based organic light emitting diodes (OLEDs), polymer light emitting diodes (PLEDs), and organic photovoltaic devices (OPVs), further improvements are still needed in providing better processing and performance. For example, one promising type of material is conducting polymers including for example polythiophenes and regioregular polythiophenes, the latter first invented by Richard McCullough. However, problems can arise with doping, purity, and solubility and processing. In particular, it is important to have very good control over the solubility of alternating layers of polymer (e.g., orthogonal or alternating solubility properties among adjacent layers). In particular, hole injection layers and hole transport layers can present difficult problems in view of competing demands and the need for very thin, but high quality, films.
A need exists for a good platform system to control properties of hole injection and transport layers such as solubility and electronic energy levels like HOMO and LUMO, so that the materials can be adapted for different applications and to function with different materials such as light emitting layers, photoactive layers, and electrodes. In particular, good solubility properties are important, as well as the control of energy levels like HOMO and LUMO and the ability to formulate the system for a particular application and provide the required balance of properties.
Polythiophenes and regioregular polythiophenes are particularly important. Background references regarding polythiophenes include (1) Sotzing, G. A. Substituted thieno[3,4-b]thiophene polymers, method of making and use thereof, US2005/0124784 A1, (2) Lee, B.; Seshadri, V.; Sotzing, G. A. Ring Sulfonated poly(thieno[3,4-b]thiophene), Adv. Mater. 2005, 17, 1792. (3) Udman, Y. A.; Pekmez, K.; Yildiz, A. Synth. Met. 2004, 142, 7. (4). Udman, Y. A.; Pekmez, K.; Yildiz, A. Eur. Poly. J 2004, 40, 1057. (5) “Method for producing soluble conductive polymers having acidic groups” EP0834885B1.
Prior art often provides however important limits such as, for example, unstable doping, lack of solubility in starting polymers, lack of versatility in formulation, lack of solvent control, limited fused systems, random sulfonation, lack of copolymerization, lack of control of molecular weight, lack of structural control and regioregularity, lack of interaction between side group and conjugated chain, and also lack of device data.